This invention relates to a bristle for a brush or the like, in particular a toothbrush, in which the bristle is made of a plastic material and includes, when viewed in cross-section, two sections with different properties.
A bristle of this type is known, for example, from German Offenlegungschrift DE 34 00 941 A1 (which appears to correspond to British application GB 2137080). This specification describes a plastic bristle having a hard core concentrically surrounded by a useful layer of a softer material. Core and useful layer may be manufactured from different plastic materials and differ in color. Attrition resulting from use of this bristle is automatically indicated to a user by a wearing down of the useful layer, exposing the different colored core. The two sections of the bristle do not, however, influence the cleaning action of a brush equipped with a plurality of such bristles.
From German Offenlegungsschrift DE 31 31 014 A1 (which appears to correspond to U.S. Pat. No. 4,382,309) a toothbrush is known with which the buccal-labial side and the lingual side of the teeth are cleaned simultaneously, enabling an improved cleaning action to be accomplished. For this purpose, the cleaning bristles of the toothbrush are shaped in the manner of two, for example, bent clusters of nylon threads with oppositely arranged ends. The cleaning bristles are manufactured by winding the nylon threads around a mandrel sufficiently often and allowing them to harden. Then the bent cleaning bristles are joined to the bristle holder of the toothbrush as by adhesive bonding.
It is an object of the present invention to provide a bristle of the type initially referred to which provides superior and gentler cleaning and is securable to a bristle holder with ease.
According to the present invention, this object is accomplished in that the sections are not in a concentric or point-symmetric relative arrangement. Basically, any distribution pattern of the sections over the cross-section of the bristle is suited to provoke the effect disclosed in the invention in which the centers of gravity (also referred to as centers of mass) of the surface areas of the sections do not coincide.
As a result of this arrangement of the two sections, the different properties of the two sections as, for example, their coefficients of expansion when subjected to moisture, heat or the like, are no longer in a position to balance each other. In consequence, the two sections expand differently, producing a curvature of the bristle along the bristle""s longitudinal axis. Thus, the bristle experiences a lateral deflection away from the bristle""s longitudinal axis.
By reason of its curvature, the bristle of the present invention also enables a gentler treatment of the object to be cleaned. Moreover, the lateral deflection of the bristle away from the bristle""s longitudinal axis has the added effect of enabling the bristle to hug the object to be cleaned better, whereby a significantly better cleaning operation can be accomplished.
It is not necessary for the bristle of the present invention to be curved by particular manufacturing methods such as winding. Instead, the lateral deflection is accomplished simply by the arrangement of the two sections with their different properties as disclosed in the invention. This affords the further advantage of enabling the bristles of the present invention to be secured in a brush also by means of conventional simple manufacturing methods.
Particularly when the bristle of the present invention is utilized in a toothbrush, for example, an electric toothbrush, a substantially improved and at the same time gentler tooth cleaning operation can be accomplished by reason of the arrangement of the two sections as disclosed in this invention and the resultant curvature of the bristle. In addition to these advantages, the curvature of the bristle enables the bristle to better penetrate the interproximal spaces, producing therein likewise a substantially improved and at the same time gentler cleaning action. A still further advantage of the bristle of the present invention is that it affords ease and economy of manufacture of such a toothbrush.
In an advantageous feature of the present invention, one of the two sections forms a circular-segment-shaped surface area, with the connecting line between the two sections being, for example, an essentially straight line, a line shaped in the manner of the arc of a circle, or a curved line. In this feature, the lateral deflection is not influenced solely by the different properties of the two sections, but also by the distribution pattern of the two sections over the cross-section of the bristle.
In an advantageous further aspect of the present invention, each of the two sections forms a semicircular surface area. In this configuration, the lateral deflection of the bristle is substantially accomplished only by reason of the different properties of the two sections. This results in a particularly good and uniform lateral deflection of the bristle away from the bristle""s longitudinal axis. Equally, this further aspect enables said deflection to be computed and thus predetermined particularly well. Finally, the configuration of the two sections as semicircular surface areas affords significant advantages in respect of bristle manufacture, in particular with a view to simplifying and standardizing the dies utilized for bristle manufacture.
On account of substantial manufacturing advantages, it is particularly suitable for the ratio of the cross-sectional areas of the two sections to have a value of between about 0.25 and about 1.0 or between 1.0 and 1.4, approximately, depending on whether the smaller or the larger are finds application as reference quantity.
In still another advantageous aspect of the present invention, the two sections have different expansion properties when subjected to moisture. In consequence, when the bristle encounters moisture, the amount of expansion of the two sections in the direction of the bristle""s longitudinal axis will differ. This produces in turn the aforementioned curvature of the bristle along the bristle""s longitudinal axis.
In particular when the bristle of the present invention is used in a toothbrush, for example, an electric toothbrush, the bristle is exposed to atmospheric humidity. The two sections of the bristle thereby expand to different degrees, producing the curvature or the lateral deflection of the bristle away from the bristle""s longitudinal axis. This results in the previously mentioned advantages in respect of the cleaning action of the bristle and the gentle treatment of the object to be cleaned by the bristle.
In another advantageous feature of the present invention, the two sections have different shrinkage properties when exposed to heat. In this feature, the manufacturing process involves the steps of heating the bristle and subsequent cooling. This results in different amounts of expansion and shrinkage of the two sections along the bristle""s longitudinal axis, causing the bristle to bend. The particular amount of deflection of the bristle away from the bristle""s longitudinal axis may be set in the manufacturing process by a corresponding heating and cooling process. It is to be noted, however, that the deflection referred to is irreversible.
In still another advantageous feature of the present invention, a filler material and/or a nucleating agent, for example, kaolin, talcum or the like is/are added to the plastic material of one of the two sections. The addition of colorants is also possible. The effect thereby achieved is that different properties are imparted to the two sections, causing the bristle to deflect away from the bristle""s longitudinal axis.
In yet another advantageous feature of the present invention, the two sections are formed of different plastic materials. This results again in different properties of the two sections, causing the bristle to exhibit a deflection away from the bristle""s longitudinal axis when in use.
In this feature, the use of different plastic materials and filler materials and/or nucleating agents may be provided alternatively or cumulatively.
It is particularly suitable in the features described to fabricate the bristle from polyamide and/or polyester. These plastic materials have proven to be particularly advantageous in particular in toothbrushes. It is possible to utilize only one of the two plastic materials to which a filler material and/or a nucleating agent is then added in one of the two sections, or alternatively, various types of one group of plastic may be used in the two sections of the bristle.
The bristle of the present invention exhibits a curvature or a lateral deflection relative to the bristle""s longitudinal axis. This produces the aforementioned advantages in respect of the improved cleaning action of the bristle and the gentler treatment of the object to be cleaned by the bristle. Further, the bristle of the present invention enables known, simple manufacturing methods to be applied without the need for elaborate manufacturing operations to obtain the curvature.
In an advantageous feature of the present invention, the amount of deflection of the bristle is in the range of between about 10% and about 90% of the length of the bristle, amounting in particular to about 50% of the length of the bristle. This has proven to be particularly suitable in practice as regards the cleaning action of the bristle.
In an advantageous further feature of the present invention, the two sections differ in color. This enables the effect of the curvature of the bristle to be seen. Particularly in the use of a plurality of bristles as in a toothbrush, a user will recognize the lateral deflection of the individual bristles from the differences in color, being thereby made specifically aware of the advantages regarding the cleaning action of the bristles.
It is particularly advantageous to utilize a plurality of the bristles of the present invention in a brush or the like, in particular in a toothbrush, in which the free ends of the bristles form a brush surface area. In this arrangement, the bristles are combined to form individual tufts of bristles constituting each a tuft surface area. The aggregate of the tuft surface areas of all bristle tufts is the brush surface area. In this case, the individual bristle tufts may fan out better, in particular in all directions, on the application of a force acting approximately in the direction of the tuft longitudinal axis. The result is a more uniform distribution of the free ends of the bristles and their lateral deflection. This deflection of the bristles is oriented in a random way, that is, there is no preferred direction for this particular deflection. Equally, by reason of the lateral deflection and the random orientation of the deflection, the individual bristles take support upon each other, reducing the possibility for the bristles to escape outwardly. Overall, an improved cleaning operation as well as a gentler treatment of the object to be cleaned is thereby accomplished.
In a particularly advantageous further feature of the present invention, the properties of the two sections of each of the bristles are dependent upon the arrangement of the bristle within the brush surface area. In other words, this means that in particular the curvature of a bristle depends upon the arrangement of this particular bristle within the brush surface area. In this manner, it is possible to provide a brush in which the curvatures of the individual bristles are adapted for the purpose of the brush, for example.
It is particularly suitable in this arrangement if the curvature of the bristles in the proximity of the outer edge of the brush surface area is smaller than that of the bristles in the inner zone of the brush surface area. This represents a particularly advantageous arrangement of the individual bristles in particular in a toothbrush. Because of the greater amount of deflection of the bristles in the inner zone of the toothbrush, the tooth surface to be cleaned is hugged and accordingly cleaned particularly well. It is also possible in this arrangement that essentially only the bristles in the inner zone of the toothbrush exhibit a curvature.
In still another advantageous feature of the present invention, the directions of deflection of the bristles are randomly distributed. This means that the deflections of the bristles of a tuft have no preferred direction. As a result, the bristle tips have different orientations, and the individual bristles bend in different directions. This is a further improvement particularly of a toothbrush with a view to the bristles hugging the tooth to be cleaned as uniformly and completely as possible. In addition, as a result of the random orientation of the bristles in different directions, one of the bristles is invariably arranged such as to enable it to penetrate the interproximal space to be cleaned particularly readily, without the need to press or turn the toothbrush against the tooth surfaces for this purpose. This results at the same time in a gentler treatment of a user""s gums by the toothbrush of the present invention.
In a method of manufacturing the bristle of the present invention, either two different plastic materials may be coextruded, or one plastic material may be coextruded while a filler material is added to a particular section. In either event, it is particularly advantageous to arrange the connecting lines between the two sections associated with the individual nozzle bores of the extrusion die in a turned relationship to each other. In this way, a random arrangement of the two sections of the bristles and thus a random orientation of the deflection of the bristles is accomplished.
Further features, advantages and application possibilities of the present invention will become apparent from the subsequent description of embodiments illustrated in more detail in the accompanying drawings. It will be understood that any single feature and any combination of single features described and/or represented by illustration form the subject-matter of the present invention, irrespective of their summary in the claims and their back-reference.